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During the actual operation of the power plant, the steam turbine will appear to operate under low load conditions. This paper proposes a novel water spray arrangement for the exhaust channel. Spraying ports are evenly arranged on the cone wall so that the direction of water spraying is opposite to that of the exhaust steam flow (reverse spraying). The feasibility of the nozzle was verified by simulation calculations of existing wind tunnel experiments. The results show that evaporation increases with decreasing load. And the evaporation volume is greater in the reverse spraying than in the down spraying (the direction of water spraying is the same as the direction of steam flow), with a maximum difference of 0.42 kg/s. The deterioration of the aerodynamic performance in the exhaust passage after water spraying can be attributed to the combined effect of the evaporation of water droplets and droplet interference with the flow field. The maximum reduction of 8.17% in the static pressure recovery coefficient in the reverse spray mode increased the total pressure drop by 377.4 Pa. After the water spraying, the temperature dropped significantly compared to before the water spraying. In reverse spraying, the vortex scale in the exhaust passage becomes larger, the return vortex flow increases, the volume absorption ability is stronger, the water droplets and steam contact time is long, good temperature reduction is achieved, and the temperature of the leaf root high-temperature zone is reduced. The maximum difference in temperature drop between the two spraying methods is 56.87 K. The results of this paper provide a reference for the cooling of the exhaust passage when the turbine is operated under low flow conditions for a long time. [ABSTRACT FROM AUTHOR]

Through the analysis of hot oil carrying theory, the problem of oil film heat accumulation in hydrostatic bearing can be revealed, so as to avoid serious lubrication failure caused by heat accumulation. In this paper, the hot oil carrying factor is defined and the mathematical model of the thermal oil carrying characteristics of the oil film is established by taking the beveled double rectangular oil pad hydrostatic bearing as the object, and the hot oil carrying law under different working conditions is obtained by changing the inclination angle of the beveled oil pad at 0.0230°, 0.0250° and 0.0280°, respectively. Theoretical calculations and simulation studies show that within the range of the circumferential inclination of the oil pad with better dynamic pressure effect of the bearing, the inclination has little effect on the oil film hot oil carrying. When the speed of the workbench is lower than 10r/min, no oil film hot oil carrying phenomenon occurs. When the speed is in the range of 10r/min-100r/min, a part of the load will cause the phenomenon of oil film hot oil carrying. And when the speed exceeds 100r/min, the heat accumulation of the oil film is the most serious at this time. There are many reasons for the lubrication failure of hydrostatic bearings, and hot oil carrying is a new research direction, this paper starts from the oil film heating mechanism of beveled oil pads hydrostatic bearings, and describes the phenomenon of hot oil carrying. [ABSTRACT FROM AUTHOR]

This document is a summary of the 14th Heat Exchanger Fouling and Cleaning Conference held in Wagrain, Austria in June 2022. The conference aimed to provide a platform for researchers in the field of heat exchanger fouling to exchange ideas and research results. The special issue includes a selection of nearly 50 papers that were preselected and peer-reviewed prior to the conference. The papers cover a wide range of topics related to fouling of heat exchangers and reflect current interests in Heat and Mass Transfer. The document also acknowledges the guest editorial and expresses gratitude to the authors and reviewers for their contributions. [Extracted from the article]

Pulsating Heat Pipe (PHP) is an emerging efficient heat transfer device, that transfers heat passively through oscillating motions of liquid slugs and vapor plugs within the device. PHP is of high effective thermal conductivity with great potential in heat transfer management for various applications. The objective of this review paper is to summarize and analyse the applications of PHP in various fields that have been reported in the open literature, emphasizing on studies reported in past half decade. The thermo-hydraulic behaviour of PHP is influenced by numerous geometric and operational parameters, which are discussed in detail in the first part of the paper. The thermal performance of the PHP under rotation condition, which is seldom discussed in previous review articles, is also discussed. These parameters act individually and in tandem to alter the performance of PHP, which makes its prediction extremely difficult. However, the benefit of numerous influencing parameters is that they can be altered to make PHP suitable for various applications. These highly variable configurations make PHP suitable for applications such as the transfer of absorbed solar energy to the location of interest, waste heat recovery, thermal management of electric vehicle batteries, fuel cells, cooling of electronic components etc. PHPs are recently being studied for applications in cryogenics and cooling of cutting tools in the machining process also. In addition, novel applications of PHP such as high-performance fins for heat exchangers, cooling of building roofs etc. are also being reported. All these applications of PHP reported in the open literature are reviewed and summarized in the present article. [ABSTRACT FROM AUTHOR]

The current paper experimentally studied the performance of solar-driven internally cooled liquid desiccant system for hot and humid climates using CaCl2 as a liquid desiccant. The system is designed to investigate the input conditions of the room by adjusting various air and solution variables. This internally cooled liquid desiccant system consists of the dehumidifier and regenerator in a single module and the regeneration of the solution is done by solar energy. The present study analyzes the effect of solution concentration, air mass flow rate and solution volume flow rate using different performance indices such as humidity reduction, moisture effectiveness, enthalpy effectiveness, and COP. The results demonstrate that the maximum moisture reduction of 4.2 g/kg d.a. is found at an airflow rate of 0.03195 kg/s, a solution volume flow rate of 12.5 LPM, and a solution concentration of 37%, while the maximum COP of 0.274 is obtained at an airflow rate of 0.0715 kg/s, a solution volume flow rate of 12.5 LPM, and a solution concentration of 37%. The maximum moisture and enthalpy effectiveness are obtained as 24.1% and 26.2%, respectively. The paper also presents the correlations for moisture and enthalpy effectiveness based on findings from experiments. [ABSTRACT FROM AUTHOR]

This paper introduces a novel a CO2 mechanical subcooling heat pump water heater (MSHPWH) to improve the heating performance in low temperatures. By utilizing a mechanical subcooling (MS) cycle, additional heat is supplied to cooling water, improving system efficiency. The study evaluates the heating COP (COPh), power consumption and temperature of hot water under various steady-state operating conditions. Results indicate that the COPh of the MSHPWH increases by 44% to 57% compared to conventional HPWH as ambient temperatures range from -25 ℃ to -5 ℃. The MS cycle proves beneficial, with a subcooling range of 4 ℃ to 20 ℃. Adjusting the refrigerant mass flow rate ratio enhances heating output and hot water temperature. Changes in the mass flow rate ratio impact COPh and the temperature of hot water concurrently. This research highlights the innovative MS cycle's significant role in enhancing CO2 heat pump water heater performance in cold climates, showcasing its potential as an eco-friendly and efficient heating solution. [ABSTRACT FROM AUTHOR]

In the context of dual-carbon strategy, the insulation performance of the gathering and transportation pipeline affects the safety gathering and energy saving management in the oilfield production process. PCM has the characteristics of phase change energy storage and heat release, combining it with the gathering and transmission pipeline not only improves the insulation performance of collecting and transporting pipes, but also extends the safe shut time during the shutdown. Proposed a thermal model of a PCM-based composite energy storage pipeline combining the character of phase transformation between PCM and crude oil has been established. The heat preservation performance of the combined energy storage pipeline was evaluated by numerical simulation.This paper analyses the heat transfer performance of complex energy storage pipes, and considers the influence of natural convection and variable temperature zone on insulation performance.On this basis, the structure design of cascade phase transition was proposed, the optimized cascading composite pipe was presented, and the performance of different insulation structures was compared. [ABSTRACT FROM AUTHOR]

This research examines the water and energy performance in wet cooling towers and identifies methods for enhancing efficiency and minimizing water and energy consumption by exploring methods to enhance system performance. A three-dimensional transient model, developed using MATLAB's open-source code software, was utilized to simulate the cooling tower's behaviour under various operating conditions. This research focuses on precise simulation of cooling tower behavior and demand modeling aided by regression. The model's accuracy was validated through experimental measurements in diverse environmental conditions. The key parameter and performance that is investigated in this paper is the temperature profile of the cooling tower, in which the performance algorithm and proposed methodologies are anchored in the operational temperature. The experimental results led to operational solutions for enhancing cooling tower performance. For winter conditions, the recommended action involves closing the upper part of the cooling tower and activating the two side fans. Specific approaches are suggested for mid-season and summer scenarios, focusing on make-up water consumption and ambient air temperature control, respectively. In addition, results indicated a close alignment between the model and the actual system, with discrepancies of less than 2% in energy consumption and 5% in water consumption. Analysis of proposed productivity enhancements and changes in supply policies indicated significant potential for energy and water conservation in wet cooling towers. Implementing these solutions could lead to an estimated annual reduction of 44% in water consumption and 4.2% in energy consumption. [ABSTRACT FROM AUTHOR]

This article is a special edition of the Heat and Mass Transfer Journal dedicated to the 14th Heat Exchanger Fouling and Cleaning Conference. The conference took place in Wagrain, Austria from June 5-10, 2022, and brought together researchers and engineers from various industries and academic institutions worldwide to discuss the importance of heat exchanger fouling research. The conference covered a wide range of topics, including fouling in hydrocarbon systems, food processing fouling, biofouling, fouling mitigation, CFD modeling, and industrial cleaning methods. This special edition of the journal includes fifteen papers focusing on fundamental research. The next conference is scheduled to be held in Portugal in April 2024. [Extracted from the article]

Microchannel heat sinks are widely used in the era of electronic equipment heat dissipation. This paper builds a numerical model of the heat sink with the interrupted rectangular microchannel and uses the experimental platform for validation. Two interrupted models including in-lined and staggered types are simulated to enhance the performance of the heat sink. The results show that the staggered type microchannels exhibit the lowest thermal resistance but the highest frictional resistance coefficient while the continuous microchannels have the opposite performance. However, the effect of heat transfer enhancement is decreasing with the increment of the interruption spacing for both of the in-lined and staggered interrupted microchannels as the overall heat transfer area is decreasing. Using the performance evaluation criterion (PEC) to evaluate the global heat transfer and flow characteristics of the heat sinks shows that the PEC of the in-lined interrupted microchannel is approximately 1.10 times higher, while the PEC of the staggered type is about 1.23 times higher compared to the continuous microchannel. This improvement is due to the interruption of the boundary layer by the cavity and the flow doping. Besides, when the Reynolds number is lower than 150, the temperature uniformity increases to roughly 1.14 times its original value. It provides a good guidance for the microchannel sink to obtain the better heat dissipation efficiency. [ABSTRACT FROM AUTHOR]

Predicting the cleaning time required to remove a thin layer of soil is a challenging task and subject of current research. One approach to tackle this problem is the decomposition into physical sub-problems which are modelled separately and the subsequent synthesis of these models. In this paper, an existing model for adhesive detachment is extended for the prediction of the cleaning time of cohesively separating soil layers. The extension is based on measurements of the pull-off forces and their correlation to the local water mass fraction. The resulting new model is validated using cleaning experiments with starch in a fully developed channel flow. Furthermore, an inhomogeneous soil distribution and its effect on cleaning results like cleaning time and removal rate is investigated. It is shown that accounting for the local soil distribution in the model leads to a significant improvement of the prediction of the cleaning behaviour. [ABSTRACT FROM AUTHOR]

Oil jet impingement cooling is the standard approach to cool high-speed high-power gears. The heat transfer between oil jets and gears is experimentally investigated in this paper. The three established methods of oil jet impingement cooling -into-mesh, out-of-mesh and inclined impingement on one of the gears- are studied. Heat transfer coefficients for these methods are experimentally determined. A loss correction approach is implemented for the evaluation of measurements. For the inclined impingement method, heat transfer on the non-impinged gear and the influence of meshing on the heat transfer coefficient are investigated. Gear meshing has an insignificant effect on the average heat transfer coefficient over the gear tooth. However, the spatial distribution of the heat transfer coefficient depends on the meshing configuration. Significant cooling on the non-impinged gear is observed with the inclined impingement method. The inclined impingement method is superior to the into-mesh and out-of-mesh methods at all measured operating points. [ABSTRACT FROM AUTHOR]

The process of heat transfer is one of the most important issues in the food industry and plays a crucial role in the storage of frozen foods. The main objective in this field is to extend the storage time, which can be achieved by limiting the heat transfer between the ambient air and the frozen food product. In this paper, the authors applied a numerical model of the phase change process to simulate the freezing and thawing process of a package wrapped with compressible multilayer polymer thermal insulation. The model was solved in COMSOL Multiphysics program and verified with experimental results with satisfactory agreement. Based on the performed simulations and experiments, it was proved that the freezing time of the tylose package is almost the same regardless of the applied film, while the thawing time of the package strongly depends on the type of film—transparent, opaque or metallized. The use of transparent film allows to extend the maximum thawing time of food products by 2 times, the use of opaque film—by about 3.7 times, and the use of metallized film—by about 4.1 times. [ABSTRACT FROM AUTHOR]

In the traditional tobacco drying process, there is often a problem of uneven drying, which is closely related to drying conditions such as air velocity and temperature. To better understand the drying characteristics of tobacco, its drying kinetic performance were experimentally studied and predicted in this paper. In the drying experiment, the range of air temperature and velocity is 20–60℃ and 0.95–4.93 m/s, respectively. The results show that the effective diffusion coefficient increases with the increase of air temperature and decreases with the increase of air velocity. The effective moisture diffusivity( D eff ) ranges from 2.077 × 10–7 to 9.136 × 10–7 m2/s. Additionally, the activation energy (Ea) is between 14.292 and 21.032 kJ/mol according to Arrhenius law. Among the six commonly used empirical correlations, the logarithmic model has higher prediction accuracy, but it has a prediction deviation of more than 20% in the later stage of drying. Based on the logarithmic model and the two models, a new prediction model of tobacco drying characteristics was proposed with a maximum relative deviation error of less than 1%. [ABSTRACT FROM AUTHOR]

The direct emission of coal mine methane caused serious environmental pollution and resource waste. To improve the methane utilization, the porous media burner was regarded as an efficient method. In this paper, the bluff body was proposed to combine with porous media to optimize the combustion characteristics. The effects of bluff body position, size and shape on the temperature distribution and gas emission were studied at different operating conditions. The results indicated that the position of the bluff body greatly influenced the combustion characteristics, and the maximum temperature of 1295 K was obtained at the position of 62 mm. The increase of the bluff body diameter promoted the flame moving to the burner outlet. And the combustion temperature increased first and then decreased when the bluff body height increased. Moreover, the CO and NOx emissions at the height of 20 mm reached 31 and 16.8 ppm respectively. The combustion temperature was significantly improved by increasing the equivalence ratio and velocity. Compared with the single porous media, the addition of the bluff body increased the combustion temperature and reduced the CO emission by 11%. [ABSTRACT FROM AUTHOR]

Miniaturization and enhanced performance of microchips has resulted in powerful electronic devices with high heat flux components. For these advanced electronics, the current heat transfer method of single-phase forced convection is reaching its thermal limit and more effective cooling solutions are needed. A pumped two-phase loop, in which a pump circulates a working fluid that evaporates to absorb heat, can offer a solution. In this paper the cooling performance of a pumped two-phase loop is discussed and validated. A numerical tool has been developed to aid in designing a fit-for-purpose pumped two-phase loop and to predict its behaviour to changing system parameters and heat inputs. Results from the numerical model are compared with temperature, pressure and flow velocity measurements obtained from a prototype setup. The effects of applying varying heat loads on both a single evaporator and on multiple evaporators simultaneously either in series or in parallel have been investigated. Heat transfer coefficients between 7 and 10 kW/m2K were obtained during the experiments. Model predictions correspond well to the measured performances and findings on the two-phase boiling behaviour are presented. The model is particularly useful for the rapid assessment of the layout of a pumped two-phase loop for high heat flux electronics cooling. [ABSTRACT FROM AUTHOR]

In this paper, a multilayer perceptron (MLP)-type artificial neural network model with a back-propagation training algorithm is utilized to model the bubble growth and bubble dynamics parameters in nucleate boiling with a non-uniform electric field. The influences of the electric field on different parameters that describe bubble's behaviors including bubble waiting time, bubble departure frequency, bubble growth time, and bubble departure diameter are considered. This study models single bubble dynamic behaviors of R113 created on a heater in an inconsistent electric field by utilizing a MLP neural network optimized by four different swarm-based optimization algorithms, namely: Salp Swarm Algorithm (SSA), Grey Wolf Optimizer (GWO), Artificial Bee Colony (ABC) algorithm, and Particle Swarm Optimization (PSO). For evaluating the model effectiveness, the MSE value (Mean-Square Error) of the artificial neural network model with various optimization algorithms is measured and compared. The results suggest that the optimal networks in the two-hidden layer and three-hidden layer models for the bubble departure diameter improve MSE by 33.85% and 35.27%, respectively, when compared with the best response in the one-hidden layer model. Additionally, for bubble growth time, the networks with two hidden layers and three hidden layers have the 44.51% and 45.85% reduction in error, when compared with the network with one hidden layer, respectively. For the departure frequency, the error reduction in the two-layer and three-layer networks is 46.85% and 62.32%, respectively. For bubble waiting time, the best networks in the two hidden-layer and three hidden-layer models improve MSE by 52.44% and 62.27% compared with the best 1HL model response, respectively. Also, the two algorithms of SSA and GWO are able to compete well (comparable MSE) with the PSO and ABC algorithms. [ABSTRACT FROM AUTHOR]

Ultrasonic field and rib surfaces are very important factors that affect the thermal performance in pool boiling. The paper has investigated the significance testing of thermal performance of the rib arrangement, the distance of ultrasonic field and the ultrasonic power in pool boiling with ultrasonic field and ribs surfaces by the orthogonal experiment. The deionized water is used as the working coolant. Then, the synergistic heat transfers and bubble motion characteristics in pool boiling are carried out at different rib arrangement, distance of ultrasonic field and the ultrasonic power by the single factor experiment. It is obtained that, compared with the single heat transfer technology of rib surface or ultrasonic field in the pool boiling, the thermal performance of compound heat transfer enhancement can be improved more significantly by combining the rib surfaces and ultrasonic field as a result of the expanded areas of heat exchange surface of rib and the cavitation effect and acoustic streaming effect of the ultrasonic field. The most significant affecting factor on the thermal performance is the rib arrangement, followed by ultrasonic power and distance of ultrasonic field. The increasing rate of heat transfer coefficient (HTC) of the best optimal scheme combination A3B3C1 with the rib arrangement of Rib II, the distance of ultrasonic field of 50 mm and the ultrasonic power of 528 W is 29.9%, which is higher than those of all the other schemes. The research results can effectively optimize the pool boiling performance of the heat transfer enhancement and provide useful support for the development of heat dissipation in related fields. [ABSTRACT FROM AUTHOR]

Hybrid nanofluids with superior thermal characteristics can be a new choice of working fluid in enhancing the heat dissipation rate of microchannels heat sink. Therefore, this paper deals with the hydrothermal characteristics of a microchannel heat sink utilizing MWCNT-Al2O3/water hybrid nanofluids. The thermal conductivity and viscosity of mono and hybrid nanofluids were measured and new experiential correlations were derived. The convective tests were carried out in three different composition ratios as well as two volume fractions of hybrid nanofluids at different Reynolds numbers. The results showed that MWCNT-Al2O3/water hybrid nanofluid at composition ratio of (80:20) and 0.05% vol. had the highest performance evaluation criteria value. [ABSTRACT FROM AUTHOR]

SCADA systems play an important role in tracking the behaviour of critical process variables and connecting geographically dispersed subsystems at the industrial plant level. This article presents a PLC and SCADA-based control framework to automate and supervise the temperature control processes in the heat exchanger plant. The OMRON (NX1P2-9024DT1) PLC is interfaced with the Wonderware InTouch SCADA system to gather data, create a simulated temperature control prototype and carry out the necessary control operations within the heat exchanger plant. The PLC controls the entire process and programming of PLC is done using Sysmac studio automation software using the ladder programming language. The proposed system controls the temperature of the heat exchanger system through PID and Fractional Order PID (P I λ D μ ) controllers with Integral Anti-windup technique. Various control strategies like Cascade Control, Feedforward Control and Smith Predictor for time delayed process are discussed for controlling the temperature of the process. The performance of both PID and fractional order PID controllers is optimized using adaptive heuristic optimization techniques like Genetic Algorithm (GA), Ant Colony Optimization (ACO) and Particle Swarm Optimization (PSO). In control system design and analysis, the calculated performance indices are used as quantitative measures for evaluating the performance of a system. The combined form of temperature controller with Cascade control, Feedforward control and dead-time compensator is modelled and examined for simulation using MATLAB. Simulation and real-time experimentation analysis of the developed controllers are executed with metaheuristic optimization techniques based on different performance indices like ISE, IAE and ITAE. [ABSTRACT FROM AUTHOR]

This article deals with the application of the temperature oscillation method (TOIRT method) to the laminar flow of water in a pipe. This dynamic and contactless method was derived for the assumption of homogeneous temperature on the fluid side, but this assumption is violated in the case of laminar flow. Numerical simulations were used to discover the fundamental influence of the amount of incident heat flux, which is modulated by the sine function, on the resulting local values of the heat transfer coefficient. The frequency of the transmitted signal, on the other hand, has no effect. The experimental measurement confirmed the numerical results even with a deviation of 25%, which is still a good result due to the sensitivity of the experimental method in this area. [ABSTRACT FROM AUTHOR]

Amputees often experience high temperatures between the amputated limb and the prosthetic socket, necessitating the use of cooling devices to mitigate this issue. However, challenges arise with the location and size of conventional heat sinks. This research proposes a novel heat sink utilising a phase change material (PCM) to dissipate heat. The leg was chosen as the site for the heat sink, designed in a cylindrical shape. Coolant flow pipes were arranged in a branched configuration inspired by constructal theory, constrained by the dimensions of the artificial leg. The degrees of freedom for the constructal design are branches akin to arterial and venous branching, aiming to minimise pressure drop. Four heat sinks with varying degrees of branching were compared based on temperature reduction, heat dissipation, pressure drop, phase change material melting capacity, and operational efficiency. The cylindrical heat sink measures 50 mm in diameter and 300 mm in length. Ice was employed as the PCM, with water served as the working fluid. The working fluid's temperature and flow rate were maintained at 40 °C and 0.2 L/min, respectively. The experimental work was prepared to validate the theoretical model. The study revealed that the proposed heat sink design, with increased branching, led to a significant temperature reduction, achieving up to 39.62%. Moreover, heat dissipation increased by 236% compared to a single-tube heat sink. The use of branched pipes resulted in a manageable increase in pressure drop, peaking at 39.9 Pa, well within pump specifications, while markedly enhancing heat dissipation. The melting time of the PCM and the melting area increased as the number of branches of the heat sink increased. Ultimately, applying constructal theory in heat sink design for PCM demonstrated its superior performance within spatial constraints, providing a promising solution for prosthetic cooling. [ABSTRACT FROM AUTHOR]

The thermocapillary motion of droplet in a vibrating fluid in a cylinder heated from the top and sides and cooled from the bottom is studied, using a three-dimensional computational fluid dynamics (CFD) model based on volume of fluid (VOF) created with Ansys-Fluent software. The outcomes support the accuracy of the Marangoni phenomenon and are in line with data published in literature. The behavior of the drop is not only impacted by the temperature difference between the top and bottom, but also by heated side surfaces and mostly by vibration. Different flow patterns are observed which directly impact the droplet's arrival time. The results proof that the neglected frequency and amplitudes of vibration in the presence of gravity have a significant and evident impact on the behavior of fluids in a zero-gravity environment. The change of vessel height also has a significant influence especially on the host fluid properties. [ABSTRACT FROM AUTHOR]

Post-dryout heat transfer plays an important role in the safety analysis of nuclear reactors or in the design of once through steam generators, and thus attracts great interest in the research community and technical applications. In the present study, experiments on post dryout heat transfer were conducted in a uniformly heated tube test section using Freon R-134a with the following range of parameters; pressure from 1.1 to 2.8 MPa, mass flux from 300 to 2000 kg/m2 s, heat flux from 20 to 140 kW/m2, and local thermal equilibrium vapor quality of more than 100%. Both procedures with increasing and decreasing heat flux were applied, to examine the hysteresis phenomenon. In general, excellent reproducibility of experiments is proven. The behavior of wall temperature and the effect of various parameters on post-dryout heat transfer can be well explained with mechanistic processes. In total, about 9000 data points were obtained and provide a valuable data base for future development of prediction models. Based on the test data gathered, five widely applied correlations of post-dryout heat transfer were selected and assessed. It was found that both correlations using thermal equilibrium approach have a much better prediction capability than the other three correlations based on thermal non-equilibrium conditions. Further analysis reveals that the main deficiency in the thermal non-equilibrium correlations is in the prediction of actual superheating of vapor, which requires obviously further improvement. [ABSTRACT FROM AUTHOR]

Apricots offer diverse health benefits, making them a valuable component of an attractive diet. In addition to ensuring the physicochemical and microbiological stability during storage and the year-round availability of this nutrient-dense fruit, apricot preservation, especially through sorption isotherm processes, also considers economic, nutritional, and environmental factors. In the same context, this study explores the analysis of two common apricot cultivars in Morocco. The primary objective is to determine the optimal conditions for storing and conserving the investigated products using the standard gravimetric static method at 30 °C, 40 °C, and 50 °C—six one-liter glass jars with insulated lids made up the experimental set-up. A fourth of the glass jar was filled with a saturated salt solution. Weighing 0.100 g (±0.001) g for adsorption and 0.200 g (±0.001) g for desorption, duplicate samples were precisely weighed and put into the glass jars. The outcomes revealed that the adsorption-desorption isotherms for all samples conformed to the characteristic Type II sigmoid pattern. The ideal water activity values to preserve "Aurora" and "Carmen" are 0.36 and 0.38, respectively. It was determined that the best model to describe the sorption curves of "Aurora" and "Carmen" was LESPAM. Analysis of the adsorption-desorption data aimed to determine the moisture content of the monolayer (ranging from 3.4 to 9.7%) and examine the properties of sorbed water within their porous structures and surfaces. [ABSTRACT FROM AUTHOR]

Water is an emerging heat transfer fluid with great promise for thermal engineering because of its heat transfer coefficients. However, much more must be done with the fluid that transmits heat to make the system more effective in handling heat. Nanoparticle cooling fluid speeds up the movement of heat through the car radiator and makes it possible to make it smaller altogether. In the present study, to examine heat transfer characteristics of nanofluids of Deionized (DI) water and Ethylene glycol (60:40). Four different concentrations of nanofluids were prepared by mixing 0.05 to 0.3 Vol. % of nanofluids with a mixture of DI water and Ethylene glycol (EG). The studies were carried out by varying coolant from 3 to 15 LPM while keeping the airspeed at a mean of 5 m/s. The airflow velocity towards the radiator is continually maintained at a median of 5 m/s. The k-type thermocouple monitors the cooling outlet's temperature and a comparative study of the thermal conductivity of experimental results with machine learning. The results show that the DI water had a lower thermal conductivity of 0.891 W/m K than the EG nanofluid, which had a thermal conductivity of 0.946 W/m K. The EG nanofluid showed a more significant heat transfer coefficient of 36384.41 W/m2 K than the DI water. The viscosity of the nanofluid increases as the concentration of nanofluid in the DI water increases and decreases as the temperature rises. [ABSTRACT FROM AUTHOR]

The study focused on examining the area-averaged heat transfer characteristics of an air jet impinging on a concave surface. The experiments involved varying the Reynolds number (Re) within the range of 10,000 to 75,000, while adjusting the jet-to-plate distance from 3 to 20 times the jet diameter (d). The experimental setup included a jet with a diameter of 11.5 mm, and concave surfaces with curvature radii of 218 mm (Curvature ratio (Cr) = 0.026) and 281 mm (Cr = 0.021) were used. A detailed investigation was conducted using Infrared Thermography to measure the average Heat Transfer Coefficient (HTC) of jet impingement on these concave surfaces. The aim was to assess the impact of surface curvature on heat transfer at different locations from the impingement point. Additionally, the research compared the heat transfer effects in circular and square impingement regions that were identical in radial span and area ratios. It was observed that the area-averaged Nusselt number (Nu) generally increased with a higher Re and a lower jet-to-plate distance ratio (z/d). A maximum average Nu increase is observed for Cr = 0.026 when the mass flow rate is from 10,000 to 75,000. Increasing the curvature is an effective approach to provide localized cooling. A correlation comparison was also conducted, and a new empirical correlation has been proposed. This correlation works effectively across various ranges of Re, z/d, Cr, and radial position (r/d) with a deviation of less than ± 11%. [ABSTRACT FROM AUTHOR]

The present study focuses on the experimental investigation and numerical study using Large Eddy Simulation (LES) for an air-impinging jet. The investigation is carried out for slot jet impingement on the heated cylinder with an adiabatic flat plate beneath the heated cylinder. The parametric investigation is conducted for parameters such as Reynolds number (Re), jet-to-cylinder spacing (h/S), surface curvature (S/D), and plate length (P/D). They are varied as Re = 10,000–25,000; h/S = 4–12, S/D = 0.072–0.108 and P/D = 0.5–2. The Nusselt number distribution over a cylinder is experimentally obtained, and to understand the impact of parameters such as Re, h/S, S/D, and P/D on it, the numerical results are extracted from LES. The Nusselt number improves with increasing Re and decreasing h/S however their impacts are different. The major influence of Re and h/S is noticeable from θ = 0°–180° and θ = 0°–90°; however, the impact of h/S is negligible from θ = 90°–180°. The Nusselt number gets enhanced with increasing S/D due to more air entrainment, which produces higher Reynolds stress and turbulence kinetic energy. The increasing plate length (P/D) shifts flow separation at a lower angular position (θ), thereby increasing the recirculation zone and reducing the attached flow region. The recirculation zone contributes to heat transfer improvement in that region. Hence, a longer plate length P/D = 2 is an ideal selection compared to P/D = 0.5 and 1 as it better facilitates the positioning of cylindrical food products with optimum heat transfer. Further, correlations are proposed for stagnation and average Nusselt numbers in terms of Re, h/S, S/D and P/D. [ABSTRACT FROM AUTHOR]

In thermal design of space applications, calculating thermal contact conductance present a challenge. The absence of convective heat transfer necessitates the essential requirement for a comprehensive of thermal contact conductance and the pivotal physical factors that influence it. This article explores a thermal management for 3U CubeSat in LEO. It covers the space thermal environment, thermal analysis methodology, and the determination of thermal contact conductance using both elastic and plastic models. The study also outlines CubeSat design considerations and the assumptions made for simulations using Comsol Multiphysics software. Experimental results from thermal balance tests are presented and compared to simulations results. The research concludes that the CMY method is the best suited for CubeSat applications to identify the thermal contact conductance, but notes the need for further refinement when dealing with materials that have high roughness or less-than-ideal contact conditions. [ABSTRACT FROM AUTHOR]

Turbo-molecular pumps are widely used in industries and scientific studies in areas such as semiconductors and sedimentation. In; such pumps, the influence of the geometric characteristics and operating conditions on performance is of interest to researchers. A single-row rotor of a turbo-molecular pump was simulated, and the test particle Monte Carlo method was used to investigate the effects of blade spacing, angle, number, and length; as well as operating conditions on performance. The maximum compression ratio and pumping speed were calculated. The pump's performance was studied for 12, 24, 36, and 48 blades in a single-row rotor at angles of 15, 20, and 30 degrees with a clearance of 0.015. We were increasing the gap from 0.015 to 0.025 and 0.035 examined across rotors with 12 to 48 blades, a blade speed ratio of 3.5, and a blade angle of 15 degrees. To validate the results, the numerical values obtained for 36 blades, 30-degree blade angle, and 0.015 clearance were compared to available experimental results, yielding good agreement. The results of this simulation are intended to cover cases of interest for design calculations. [ABSTRACT FROM AUTHOR]

The present study elucidates the experimental investigations on a novel flexible heat transfer device that can be used in a wide range of modern electronic device cooling applications which demand flexibility. The objective of the present is to address the challenges encountered by current flexible heat transfer devices, including concerns related to out-gassing and the permeation of non-condensable gases. These issues ultimately contribute to the deterioration of the long-term dependability of such devices. The present study provides an analysis of the steady-state performance of the flexible heat transfer device under various heat loads and orientations (0°, 45°, and 90° angles). Using COMSOL Multiphysics 6.1, numerical simulations are performed to explain the dynamics of heat transfer of the flexible heat transfer device developed. The performance is evaluated in terms of thermal resistance, equivalent thermal conductivity, and average temperature difference across the evaporator and condenser. Under steady-state operation, it has been determined that the flexible heat transfer device exhibits a minimum thermal resistance of 2.3 °C/W. Additionally, a maximum effective thermal conductivity of 2407 W/mK has been reported for a bending angle of 45°, which is six times more than relevant flexible heat transfer devices, such as copper thermal straps. [ABSTRACT FROM AUTHOR]

This work proposes a novel flat heat pipe technology, namely the rod-plate heat pipe, formed by the diffusion bonding of a set of parallel rods, of around 8 mm diameter, between flat plates of approximately 500 × 60 × 2 mm3. This design is inspired by the mini wire-plate heat pipe concept. This work is the first in the literature to apply this technology to large size heat pipes. A theoretical model is devised and used to predict the fluid distribution along the heat pipe, detect regions of flooding and dry-out and determine the best charging volume. Experiments are performed with a stainless-steel device operating in horizontal orientation with water as working fluid. Electrical cartridge resistances play the role of the evaporator heat source, while the condenser is cooled by either natural convection and radiation or heat exchangers linked to a thermal bath. For the experiments using a device with an exposed condenser, the minimum thermal resistance is 0.147 °C/W, for 88.50 W for heat input. The operation temperature increases with heat input up to 326.56 °C for a heat load of 191.40 W. The thermal resistances of the heat pipe cooled by heat exchangers have a minimum of 0.123 °C/W at 171.57 W heat transport rate, for a 40 °C thermal bath temperature. The theoretical results and data obtained so far corroborate the feasibility of this technology, with devices able to transfer up to 22.18 W per groove. [ABSTRACT FROM AUTHOR]

The rapid fluctuations in heat transfer rates make it challenging to determine the surface temperature history and the estimation of accurate heat generation in research applications such as IC engines, gas turbines, and high-speed space vehicles. Therefore, thin-film heat flux sensors (TFHFS) are generally used to measure the heat flux in such applications due to their high sensitivity and quick response time. The present study demonstrates that increasing the annealing heat treatment temperature will enhance the adhesion of the thin film and the capabilities of these hand-made TFHFS for transient measurements at low temperatures and for short periods. In the present work, TFHFS is fabricated in-house using platinum as a sensing element and Macor as an insulating substrate. The sensitivity (S) and temperature coefficient of resistance (TCR) are estimated using an oil batch calibration technique. At the same time, the performance of TFHFS is tested in a dynamic convective environment. The TFHFS is exposed to the convective environment using a designed calibration set-up, and their transient heat fluxes are computed by conducting several trials. Additionally, the numerical solution has been accomplished using various experimental parameters. In comparison to the outcomes of the experimental method, it is observed that the average fluctuating temperature and mean surface heat flux have an inaccuracy of 0.33% and 4.17% respectively. [ABSTRACT FROM AUTHOR]

Calculating a two-phase pressure drop is required in many fields. A general and accurate correlation is still needed, although numerous studies of frictional pressure drop correlations have been conducted. Therefore, a wide range of experimental data points were collected on the two-phase pressure drop of smooth tubes, 2012 points, covering 16 refrigerants with tube diameters ranging from 1.88 to 12 mm. The experimental data points were compared and evaluated with nine widely used correlations and models. The results show that the (Kim and Mudawar in Journal of Int J Heat Mass Transf 55:3246-3261, 2012) correlation gives the best prediction, followed by the Wang et al. (Exp Therm Fluid Sci 15:395–405, 1997) correlation and Friedel (European Two-Phase Flow Group Meeting, Ispra, Italy, 1979) correlation with mean deviations of 26.94%, 27.26% and 29.76%, respectively. A general two-phase frictional pressure drop correlation is proposed. The proposed correlation is validated against the database and compared with other correlations. The proposed correlation agrees better with the database than the others, with an absolute mean deviation of 19.84%. [ABSTRACT FROM AUTHOR]

A new clamp-on power ultrasound solution is being developed for tubular heat exchangers (HX). This system features software-controlled ability to guide the cleaning effect, to reach also the most challenging locations. The new solution was evaluated by finite-element simulations, and field tests are being carried out on tubular HX. Preliminary results show that the new solution is capable of fouling prevention. The results suggest good potential also for fouling cleaning. In conclusion, the new software-guided clamp-on power ultrasound solution was proven valuable since it permits on-site fouling mitigation, without process interruptions, and by increasing the physical cleaning cycle of tubular HX. The solution will thus result in significant savings in equipment and maintenance costs as well as decreasing energy and production losses. [ABSTRACT FROM AUTHOR]

Efficient heat transfer is essential for the economically sustainable operation of heat exchangers. Therefore, the internal flow is influenced systematically in various ways, for example by introducing macrostructures on the pipe surface. Since these measures may negatively affect the cleanability of the heat exchanger, it is necessary to investigate not only the increase in heat transfer, but also their impact on cleaning processes. For this purpose, the cleaning of sour milk in dimple-structured pipes is investigated experimentally. Both macroscopic and microbial cleaning tests are conducted to assess the influence of the surface's macrostructure on cleanability. Two geometry variations of dimple-structured pipes are investigated and compared to a straight pipe Although fouling is enhanced by the dimple structures, a higher macroscopic cleaning rate can be achieved with the optimized dimple. Moreover, the residual microbial contamination decreases significantly due to the introduction of dimples. All in all, the cleaning experiments confirm the positive influence of the dimple structures on cleanability. [ABSTRACT FROM AUTHOR]

Fouling in refinery equipment occurs predominantly by corrosion, chemical reaction, asphaltene precipitation or coke formation depending on prevalent operating conditions. Iron sulphide formation via a corrosion mechanism on metallic surfaces has been identified via past studies to precede coke formation. These studies however have been carried out at temperatures where coke formation blankets the sulphide layer (>350 °C). The present study reports results from experimental investigations conducted to understand crude oil corrosion fouling on a heated surface in a temperature range where this fouling mechanism is expected to be largely prevalent and not blanketed by other mechanisms (<300 °C). Experiments were conducted using a High Temperature Variable Shear (HTVS) coupon test rig. The test runs covered a wide range of fluid bulk temperatures and stirrer speeds (which incorporated a shear effect), ranging from 250 to 300 °C and 100 to 600 RPM respectively. Parts of the foulant deposits collected were found to strongly (hard) and weakly (soft) adhere to a coupon surface. These deposits were subsequently characterized using Thermogravimetry (TGA), Elemental analysis, Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The nature of soft deposits was found to be distinct from the nature of crude oil used. The formation of hard and soft deposits on a Carbon Steel (CS) and Stainless-steel (SS) surface was investigated. Based on the data obtained, a mechanism is proposed to explain the underlying fouling phenomena. [ABSTRACT FROM AUTHOR]

A key challenge in interpreting test rig fouling data is separating the measured overall heat transfer into a convective and a conductive contribution. In fouling rig tests, the change in convective resistance relative to the fouling resistance can be substantial. In the field, this impact is less significant and typically not accounted for. Methods and models are presented to improve translating test rigs data to the field. To account for these effects, the measured thickness and roughness of the fouling deposits at the end of the test are used to back-calculate a thermal conductivity of the deposit, which is then assumed constant over the test duration. With the assessed thermal conductivity, the heat transfer and pressure drop models can be reconciled to measurements by solving for the deposit thickness and roughness at each timestamp. Presented results also include the estimated deposit surface temperature, convective heat transfer coefficient, and the deposit's conductive resistance. This new information can be used to develop a fouling model and improve the assessed rate. A description and demonstration of this technique are provided. [ABSTRACT FROM AUTHOR]

Shell-and-tube heat exchangers (STHE) are widely used in the process and energy industry. Maldistribution and the often resulting fouling in these STHE cause additional energy consumption and lower production throughput. Increased average wall shear stress, compared to that of the maldistributed case inside the tubes is expected to mitigate fouling. This can be achieved by a uniform distribution into the tubes. Field and laboratory data suggest that common crude oil fouling is profoundly mitigated above 10 Pa and is significantly reduced above a wall shear stress of 15 Pa [1]. Many STHE already have lower design shear stresses than those mentioned. Therefore, if maldistribution takes place, tubes with less flow velocity will have even more fouling. To investigate tubeside flow maldistribution, a parametric STHE model is studied with computational fluid dynamics (CFD). At first, a comparison between the standard k- ϵ -model and the new standard SST-model is performed to check if SST could provide improved simulation results. Afterward, a range of geometrical parameters will be investigated to find influencing quantities of maldistribution. The resulting velocity distributions are visualized and evaluated by using different statistical approaches. At least, a sensitivity analysis will be done to show how each parameter influences the tubeside flow distribution in STHE. [ABSTRACT FROM AUTHOR]

Water chemistry plays an important role in fouling kinetics and morphology. This work investigates the influence of zinc cations in potable water, specifically the kinetics of crystallisation and their effect on the fouling layer during the operation of a batch steam generator system and a once-through flow system. The kinetics of precipitation in the batch crystalliser were examined based on the change in concentration of the foulants, while the fouling resistance approach was used in the flow system. In addition, morphological testing was carried out using Scanning Electron Microscopy, Powder X-ray Diffraction, and Energy dispersive X-ray. The findings showed that the precipitation rate of calcium carbonate decreases with the increase in zinc ions until reaching the zinc carbonate supersaturation in the water due to water evaporation. Regarding morphology, co-precipitation of zinc carbonate was observed at high zinc concentrations. As a result, a double effect was observed where zinc both retarded and enhanced fouling over time. The fouling rate in the flow system decreased as the zinc concentration increased. Zinc ions were found to influence the morphology of deposit minerals significantly. Moreover, the surface deposition of zinc salts increased with the solution content of zinc. [ABSTRACT FROM AUTHOR]

In this work, we compared thermal conductivities of polypropylene fibers and fibrils. The polypropylene fibers were melt spun, and oriented by solid-state drawing. Both wide-angle X-ray scattering and sonic velocity measurements were performed to determine the orientation of fibers. The thermal conductivities of fibers were measured via direct electrical heating method, and that of fibrils were measured via thermal bridge method. Our results show that the thermal conductivity of polypropylene fibers increases linearly with their sonic velocity. This suggests we can use the sonic velocity to characterize the thermal conductivity of semicrystalline polymers. Our results also indicate the average thermal conductivity of fibrils is close to that of fibers. This implies that the low thermal conductivity of polymer fibers is due to the low thermal conductivity of fibrils, instead of thermal resistance between fibrils. [ABSTRACT FROM AUTHOR]

Natural convection condensation, with the advantage of high reliability and not requiring complex mechanical drive structures, is broadly used in industrial fields, such as chemical, nuclear power, automotive, etc. This work aims to investigate the heat transfer mechanism and evaluate the performance of natural convection condensation with the artificial neural network (ANN) method, correlation predictions, and the code based on the boundary theory. An empirical correlation was proposed based on the present experimental data with operating conditions in the pressure range of 0.2 MPa -0.6 MPa, subcooled temperature range of 11 K–45 K, and air mass fraction range of 0.0049–0.69. The empirical correlation was validated against a consolidated database, with 91% of the data reproduction falling within the error band of ± 30%. An ANN model was put forward with training, validation, and testing using the present experimental data, which yields an error of ± 5% in the present test data. When the trained model was utilized to reproduce the additional database, all the data fell within an ± 11% error band. Finally, a side-by-side comparison in heat transfer coefficient reproduction was conducted among those rapidly computational methods, and the ANN model turned out to have the best performance. [ABSTRACT FROM AUTHOR]

The experimental study concerning new two and three dimensional mini heat pipes, proposed for cooling electronic components in printed circuit boards is presented. These heat pipes can capture the heat from electronic components and conduct it to the cabinet wall, through the narrow spaces available between boards. As the location and dissipation of the electronic components vary, several different heat pipes are necessary for a complex electronic equipment, which should operate at different temperatures and orientations. A hybrid wick structure, composed by sintered copper powder and wire-plate technologies along the device are proposed. Four different types of hybrid mini heat pipes, in up to three generations, were designed and constructed, using diffusion bonding fabrication technique. Two different testing setups were developed. First, the thermal performance of the hybrid heat pipes was accessed, resulting in the selection of the appropriated working fluid and its volume. Second, the devices were tested in rigs that mimic actual electronic equipment geometries and operational conditions. The several hybrid multidimensional heat types worked well, even against gravity. Besides, the present work shows that the wire-plate wick structure, up to this date considered only in academic studies, resulted in very flexible heat pipes, able to start up easily, in several adverse geometric and gravitational conditions, especially when combined with more conventional technologies, such as sintered porous media. Besides, the fabrication process developed that includes diffusion bonding, can be considered a novelty. [ABSTRACT FROM AUTHOR]

This study investigates the comparative analysis performance of three environmentally friendly refrigerants, R1270, R290, and R600a, in the context of flow boiling heat transfer (FBHT) and pressure gradients. The experiments employ copper microfin and smooth tubes, operating under varying conditions, including saturation temperatures (Tsat) of 6 and 15 °C, heat fluxes (HF) ranging from 13 to 30 kW.m−2, mass fluxes (MF) spanning 187 to 427 kg.m−2.s−1, and vapor quality from 0.1 to 1.0. Both tube types share identical dimensions - an outer diameter, inner diameter, and length of 7 mm, 6.14 mm, and 500 mm, respectively - facilitating a focused investigation into the impact of microfins on flow boiling characteristics. The results highlight noteworthy differences among the refrigerants, with the microfin tube exhibiting substantial enhancements in heat transfer coefficient (HTC), particularly pronounced with R1270 and R290. At the same time, the R600a demonstrates more HTC improvements than the smooth tube. Additionally, the microfin tube increases pressure gradients. The average enhancement factor (EF) for R600a, R290, and R1270 are 2.15, 1.95, and 1.9, respectively, while the average penalty factor (PF) for R600a, R290, and R1270 are 1.25, 1.3, and 1.35, respectively. Comparative analyses with established literature correlations validate the experimental findings. [ABSTRACT FROM AUTHOR]

Geometry optimization aims to maximize heat transfer rate and minimize pressure drop attending to structural and fabrication constraints. The present work carried out the first optimization study of compact heat exchangers produced by selective laser melting (SLM) with circular channels. No optimization study investigated circular mini channels since most focus on semi-circular channels of printed circuit heat exchangers. Besides, since samples produced by selective laser melting present higher yield strength, it was possible to investigate a higher range of configurations. Analytical models of heat transfer and pressure drop, with structural analysis in finite element model were used in the optimization study. The analysis was conducted using genetic algorithms (NSGA-II) based on evolutionary and dominance concepts to evaluate different configurations. The results showed a strong relationship with the admissible stress limit, so a new study, using the properties SLM samples, was performed. Decision variables' behavior was investigated among all the optimum solutions, besides stress constraint and flow type (cross and counter-flow), resulting in different optimal solutions of Pareto curves. The optimization provided heat transfer and pressure drop ratio from 1.2 kW/Pa to 12.5 kW/Pa. The optimized arrangements were compared with heat exchangers from the literature, demonstrating a 19% improvement in thermal performance and an 85% reduction in pressure drop. [ABSTRACT FROM AUTHOR]

Liquid jet quenching of metals is typically adopted to achieve specific material properties of metals, thereby making them suitable for advanced engineering applications. In this process, a metal plate is heated and cooled rapidly by impinging water jets. The temperature history during cooling leads to a microstructural transformation thereby improving the material properties such as hardness. During liquid jet quenching, since the plate surface temperature is above the Leidenfrost temperature, the boiling heat transfer dominates. This is associated with an intense cooling and water vapor generation, where the Leidenfrost effect impedes the immediate wetting of the surface. The resulting uneven cooling over the plate surface tends to potential deformation and cracking. To control this process, a detailed understanding of the spatial and the temporal heat transfer behavior is imperative. Experiments in this context are limited and therefore investigating the conjugate heat transfer process is to be combined with a multi-phase numerical model. The two-phase numerical model based on the Euler-Euler approach is developed and validated to simulate the jet quenching of a stationary plate considering all the boiling regimes within a single framework. This model consists of two phases, the liquid water which is the continuous phase (primary) and the water vapor modeled as the dispersed phase (secondary). In this study, a circular water jet (tap water) impact is considered and the plate materials under investigation are aluminum alloy (Al-alloy) and stainless steel (St-steel). Experiments are performed using infrared and high-speed imaging. The validated numerical model provides the technical parameters such as wetting front behavior, heat flux, HTC (heat transfer coefficient) etc. The influence of the jet Reynolds number and the plate material properties on the heat transfer is analysed. The study emphasizes that the plate material has a significantly higher influence on the heat transfer during jet quenching. [ABSTRACT FROM AUTHOR]

The direct contact evaporation of n-pentane volatile liquid drop in a warm flowing immiscible liquid (water) has been investigated experimentally. A Perspex column with a 10 cm internal diameter and 100 cm active height was used in the experiments. N-pentane at its saturated temperature (~36 °C) and distilled warm water were utilised as a continuous and dispersed phase. The warm water, with three different Jacobs numbers (Ja), (Ja = 6.1, 23 and 46.3), flows from the top of the column and leaves from the bottom at three different Reynolds numbers (Re = 3250, 6500 and 9750). The evaporation of the drop while rising along the column was filmed with a Photron FASTCAM high-speed camera ( 65,000 f/s). All images were analysed using AutoCAD, and the two-phase bubble, the vaporisation ratio and the half-opening vapour angle were measured. The convective heat transfer coefficient in terms of Nusselt number (Nu) was predicted based on the measured two-phase bubble radius through the experiments. The effect of Reynolds's number (Re), Jacobs's number (Ja), vaporisation ratio (x), and diameter ratio (B) on Nu were investigated. The experimental results revealed that Nu increased with time. The Re and Ja significantly affected the time-dependent Nu. Although the final Nu was nearly the same for all cases (Nu = 21), the higher the continuous phase Re, the higher the Nu, especially with the progress of evaporation . In addition, the results showed that Ja inversely influenced the average Nu, and the final value of Nu depended strongly on Ja. The higher the Ja, the lower the average Nu and the shorter the time for complete evaporation. In this regard, the dimensionless time required for complete drop evaporation was about 38, 60 and 120 for Ja of 46.3, 23 and 6.1, respectively. [ABSTRACT FROM AUTHOR]

Previous studies have demonstrated that altering the surface structure can enhance heat transfer. In this study, a square micropillar array with a homogeneous structure was designed for a long rectangular channel with a hydrodynamic diameter of 10 mm. Deionized water and HFE-7100 were used as working fluids for the study. The effect of flow rate and subcooling degree on flow boiling heat transfer performance is discussed. The bubble behavior of two different media was compared by visualization experiments. The results show that the square microcolumn array will delay the ONB point by increasing the heat transfer area and disturbing the main fluid, and improve the overall boiling heat transfer performance by 2–3 times. It was found that HFE-7100 boils better under low heat flow density, but its stable nuclear boiling time is shorter. Furthermore, the effects of volume flow and subcooling on heat transfer performance vary significantly at different stages of the boiling process. Before the ONB point, an increase in volume flow will increase the heat current density by 88.9% and reduce the boiling heat transfer stability. After the ONB point, the effect of fluid flow on the boiling process weakens. [ABSTRACT FROM AUTHOR]

A potential solution to environmental problems associated to the use of fossil fuels and the exploitation of natural resources for energy production is the development of renewable energies with greater capacity, adaptability and integration, as well as their use for the improvement of this systems. Researchers turned their attention to biological and natural processes such as honeycombs at a structural level to increase the mechanical properties of various technologies. This investigation shows the results of the thermal analysis of a novel solar collector designed based on a Honey-Comb conjecture studied under different connections. Several structures were proposed considering a serial and parallel connections. Each one was designed and simulated in SolidWorks® software Flow Simulation. The study considers different boundary conditions as mass flow and solar radiation on the surface of the collectors. In the analysis, the maximum temperature was achieved at the highest solar radiation of 1050 W / m 2 and the lowest flow mass of 0.052 kg/s. On the other hand, the peak performance of the heat thermal parameter in the whole study was achieved at solar radiation of 1050 W / m 2 and the maximum mass flow of 0.17 kg/s. A honey-comb structure conformed by three collectors (AC1) shows an increase of around 187%, against a single collector (A0), comparing the other structures two collectors in series (AS1) and two collectors in parallel (AP1) connections the total increase in the useful heat obtained with AC1 was 52% and 49% respectively. [ABSTRACT FROM AUTHOR]

This work aims to use experimental data from thermal characterization and adsorption/desorption isotherms of two tropicals woods species (Ayous and Tali) to propose an empirical model of thermal conductivity as a function of air relative humidity. A static gravimetric method was used to determine the adsorption isotherms of Tali and Ayous at 30 °C, and 40 °C. The GAB, Henderson and Nelson models were used to predict the isotherms. Exponential models of thermal conductivity and volumetric heat capacity with air relative humidity were proposed. The influence of hysteresis phenomenum was studied on these properties. The reliability of the developed empirical correlation between thermal properties and air relative humidity was evaluated by comparing the experimental and predicted curves. The relative errors were less than 8% for both Ayous and Tali. The correlation coefficients obtained were greater than 99% for both species in adsorption and desorption. There was also an increase in the equilibrium water content of both species with the increase in water activity at constant temperature. The correlation coefficients between GAB model and sorption experimental data were lower than 99% when Ayous was subjected to a temperature of 40 °C in adsorption and Tali to a temperature of 40 °C in desorption. [ABSTRACT FROM AUTHOR]